1. Field of the Invention
The present invention relates to the field of manufacturing control devices and, more particularly, to a process gas controller for use in semiconductor processing.
2. Prior Art
In the manufacture of semiconductor integrated circuit devices, various circuit elements are formed in or on a base substrate, such as a silicon substrate. Various processes for forming these integrated circuit devices are well known in the prior art. In performing some of these steps, a semiconductor wafer is placed in a reactor chamber in order for the wafer to undergo certain necessary processing steps, which may include steps for depositing or etching various layers of the wafer. After these wafers are loaded into a given chamber, the wafer is subjected to one or more of a variety of gases, liquids and/or plasma during a given process cycle period. In order to ensure proper processing of these wafers, a number of chamber parameters must be tightly controlled. One critical parameter is the amount and composition of the fluid introduced into the chamber for a given processing step.
In order to control the amount and composition of the fluid being introduced into the processing chamber, various tools and schemes have been devised to control the fluid flow to the reactor chamber. One commonly used device is a mass flow controller, which controls the amount (mass) of the fluid being introduced into the chamber.
Most prior art mass flow controllers typically require an external control box to generate a set point signal for gas control, and provide the power for the sensor electronics and the control valve. The mass flow controller adjusts the flow control valve opening so that the flow through the flow sensor matches the set point valve provided by the controller. Most of these control boxes are provided with a computer interface to integrate the mass flow controller into an automated process control system.
Although the prior art technique may be adequate for many prior art processing techniques, it has significant drawbacks for state of the art techniques for fabricating devices utilizing submicron technology. The state-of-the-art submicron technology, utilized for manufacturing devices which have device dimensions and/or line dimensions of less than 1 micron, require that reactor chamber tolerances be controlled to much tighter specifications, which one specification is the amount of the gas being introduced into the chamber.
The characteristics of prior art mass flow controllers change with time due to aging and can result in increasing errors in the gas flow. Aging of any of three elements:&gt;the flow sensor, the mass flow controller's on-board electronics, and the control valve can cause mass flow controller drift. In addition, with some corrosive or reactive gases, critical flowmeter dimensions can be changed which will also cause mass flow controller drift.
Accordingly, it is appreciated that the self-correcting mass flow controller, which can correct the mass flow of the fluid to the chamber during use, will provide a more reliable mechanism to control the fluid provided to the processing chamber.